Field of the Invention:
The present invention relates to a displacement detection apparatus using a grating interferometer.
Description of the Related Art:
Conventionally, there is widely used, as the measuring instrument that performs accurate measurement of a linear displacement or a rotational displacement, an apparatus that optically performs displacement measurement by the use of a grating having a periodic light and dark pattern or a periodic unevenness formed therein and a light source such as an LED. In recent years, a high-resolution displacement detection apparatus capable of measuring the displacement equal to or less than 1 nm has been required especially in semiconductor manufacturing equipment.
The examples of such a conventional type displacement detection apparatus include the one described in, for example, Patent Literature 1. In the displacement detection apparatus described in Patent Literature 1, the light emitted from a light source is caused to vertically enter a diffraction grating to thereby generate two diffracted light beams. Furthermore, the diffracted light beam is again caused to thereby enter the diffraction grating to generate twice-diffracted light beam. Then, the two twice-diffracted light beams are superimposed to give interference light beam. Then, a displacement of the diffraction grating is detected by receiving the interference light beam by the use of a light-receiving element.